Miscible polymer blends containing poly(2-alkyl-2-oxazoline)

ABSTRACT

Miscible blends of poly-2-oxazolines and thermoplastic polymers are disclosed herein. These blends exhibit a single glass transition point indicative of a miscible blend. The blends of this invention are useful as membranes, particularly separation membranes for mixtures of organic compounds or organic compounds and water and a pervaporation process.

BACKGROUND OF THE INVENTION

This invention relates to blends and alloys of polymers of 2-oxazolines,and to articles, particularly membranes, prepared therefrom.

Polymers of 2-oxazolines are generally hydrophilic water-solublematerials. Such oxazoline polymers have proven utilities as adhesionpromoters and viscosity modifiers in similar applications.Unfortunately, however, such oxazoline polymers when formed into solidarticles such as films exhibit very poor mechanical properties and showsensitivity to atmospheric moisture. Dried films of oxazoline polymersare too brittle to be useful in most applications. Water causesdissolution of such articles and films.

Despite these mechanical problems which limit the utility of oxazolinepolymers, said polymers have many desirable properties such ashydrophilicity which would be advantageous in many solid articles suchas films. It would therefore be desirable to prepare solid articlescontaining oxazoline polymers which exhibit good mechanical and physicalproperties.

Oxazoline polymers have previously been employed in small amounts asadditives in water-insoluble polymer compositions. In addition, polymersof oxazoline have been blended with polyolefins to form immiscibleblends. However, it is not heretofore been attempted to prepare blendsor alloys of oxazoline polymers and other polymers comiscible therewith.

SUMMARY OF THE INVENTION

In one aspect, the present invention is a blend or alloy of a firstpolymer which is a polymer of a 2-oxazoline and at least one otherpolymer which is not a polymer of a 2-oxazoline, wherein said otherpolymer is miscible with said first polymer in the relative proportionsthereof present in said blend or alloy, and wherein the weight ratiosaid first polymer to said other polymer present in said blend or alloyis from about 19:1 to 1:19, preferably from about 9:1 to 1:9.

In another aspect, this invention is a semipermeable membrane comprisinga blend or alloy of a first polymer which is a polymer of a 2-oxazoline,at least one other polymer which is not a polymer of a 2-oxazoline andwhich other polymer is miscible with said first polymer in relativeproportions thereof present in said blend or alloy and wherein theweight ratio of said first polymer to said other polymer present in saidblend or alloy is from about 19:1 to about 1:19, preferably from about9:1 to about 1:9.

Surprisingly, it has been found that miscible blends of 2-oxazolinepolymers are prepared with a variety of other polymers. The miscibilityof 2-oxazoline polymers with such polymers is unexpected in light of thediverse structures and properties of the component polymers, especiallythe differences in solubility characteristics.

Also surprising is that even though these blends contain substantialamounts of 2-oxazoline polymers, the 2-oxazoline polymer is notextractable from the blend in significant quantities when the blend iscontacted with water. Accordingly, these blends can be used inapplications which require contacting the blend with an aqueousenvironment.

In addition, in many cases the blends of this invention exhibit improvedphysical properties as compared to the 2-oxazoline polymer alone.

The blends of this invention exhibit utility as membranes, particularlyas pervaporation membranes for use in separating components of liquidmixtures such as water/ethanol or ethanol/hexane mixtures. Membranescomprising the blends of this invention exhibit particularly highselectivities and/or fluxes as compared to corresponding conventionalpermeation membranes.

DETAILED DESCRIPTION OF THE INVENTION

The 2-oxazoline polymers employed herein are polymers containing pendantN-acyl groups, as represented by the structure (I). ##STR1##

Such 2-oxazoline polymers are readily prepared by the ring openingpolymerization of 2-oxazolines or like compounds, represented by thestructure (II) ##STR2## wherein R is hydrogen or an inertly substitutedlower alkyl group; R¹ is typically hydrogen, inertly substituted phenylor an inertly substituted lower alkyl; and X is 1 or 2. The substituentsand subscripts are hereinafter defined. The ring-opening polymerizationof 2-oxazoline monomers is generally conducted in the presence of acationic polymerization catalyst at a reaction temperature of about0°-200° C. Typical catalysts include strong mineral acids, organicsulfonic acids and their esters, acidic salts such as ammonium sulfate,Lewis acids such as aluminum trichloride, stannous tetrachloride, borontrifluoride and organic diazoniumfluoroborates, dialkyl sulfates andother like catalysts. This ring-opening polymerization is furtherdescribed by Tomalia et al., J. Polymer Science, 4, 2253 (1966); Bassiriet al., Polymer Letters, 5, 871 (1967); Seeliger, Ger. 1,206,585; Jonesand Roth, U.S. Pat. No. 3,640,909; and Litt et al., U.S. Pat. No.3,483,141.

The polymer obtained in the polymerization of 2-oxazoline is linear,N-acylated polyalkyleneimine having a molecular structure consisting ofrepeating units (I). If desired, a portion of said N-acyl groups may behydrolyzed. Generally, hydrolysis of such N-acyl groups tends todecrease the miscibility of the 2-oxazoline polymer with the otherpolymer employed herein. Accordingly, it is typically not desirable toemploy a 2-oxazoline polymer having greater than 25 number percent ofsuch N-acyl groups hydrolyzed. Preferably, fewer than 10 number percentof such N-acyl groups are hydrolyzed.

The term 2-oxazoline is used herein to describe compounds having thegeneral structure as defined by II, including species wherein x is 2.The term "inertly substituted" means that the moiety referred tocontains no substituent group which interferes with the polymerizationof the 2-oxazoline, or to the ability of the polymer to form a miscibleblend with said other polymer.

Illustrative inert substituents include alkenyl, hydrocarbyl, alkoxy andthe like. Exemplary R substituents include hydrogen, methyl, ethylN-propyl and exemplary R¹ substituents include hydrogen, methyl, ethyl,propyl, pentyl, cyclohexyl, and the like.

Preferably, x is 1, each R is hydrogen and R¹ is a lower alkyl group,especially an ethyl group. The 2-oxazoline is most preferably2-ethyl-2-oxazoline. The most preferred 2-oxazoline polymer ispoly(2-ethyl-2-oxazoline) which is non-hydrolyzed.

Typically, the 2-oxazoline polymer has a molecular weight within therange of 1,000 to 1,000,000. In the present invention, it is preferableto use a 2-oxazoline polymer having a molecular weight within the rangeof about 100,000 to about 600,000.

The 2-oxazoline polymer is incorporated into the other polymer by anyknown blending technique such as conventional melt blending equipment,including compounding extruders, Banbury mixers, roll mills and thelike, as well as by solution blending in a suitable solvent.

The oxazoline polymer is blended with at least one other polymer whichis not a polymer of a 2-oxazoline. Said other polymer is water-insolubleand capable of forming a miscible blend with the oxazoline polymer.

A "miscible blend" as that term is used herein refers to a blend of anoxazoline polymer and at least one other polymer which blend exhibitsonly one glass transition temperature (T_(g)). By contrast, blends ofpolymers which are immiscible exhibit the characteristic T_(g) 's ofeach component of the blend. If such polymers form a miscible blend, theT_(g) of the individual components are not exhibited by the blend.Instead, the blend exhibits a characteristic T_(g) of its own.

Procedures for determining the T_(g) of polymers or blends of polymersare well known in the art. Differential Scanning Calorimetry (DSC) is anespecially suitable technique for measuring T_(g).

The other polymer employed herein does not necessarily form miscibleblends with the oxazoline polymer in all proportions. It is recognizedthat certain polymers form miscible blends with oxazoline polymers onlywhen blended therewith within a limited range of proportions. Blends of2-oxazoline polymers with such other polymers are considered to bewithin the scope of this invention when such blends are miscible blendsas defined herein.

Exemplary polymers which form comiscible blends with polymers of2-oxazoline in a wide range of proportions include certainstyrene/acrylonitrile copolymers; rubber modified styrene/acrylonitrilepolymers; phenoxy resins; certain styrene/acrylic acid copolymers andthe like. Polymers which form miscible blends with polymers of2-oxazoline in a narrower range of proportions include, for example,polyvinylidiene chloride; copolymers of vinylidiene chloride and vinylchloride; and styrene/acrylic acid copolymers containing small amountsof acrylic acid.

Styrene/acrylonitrile copolymers (SAN polymers) which are prepared froma monomer mixture containing from about 18 to about 50 percent by weightacrylonitrile form miscible blends with polymers of 2-oxazolines in allproportions. Any of such SAN copolymers having such acrylonitrilecontent may be employed herein. Exemplary SAN polymers are commerciallyavailable from The Dow Chemical Company under the TYRIL® brand name.

In addition, rubber-modified SAN polymers are useful herein. Such rubbermodified SAN polymers typically comprise a continuous matrix of SANpolymer having colloidially sized rubber particles dispersed therein.Said rubber particles generally have a volume average particle diameterof less than 1 micron, perferably less than about 0.5 micron, morepreferably between 0.05 and 0.5 microns. Said rubber particles comprisea natural or synthetic elastomeric polymer which is preferably a polymerof a conjugated diene monomer such as isoprene or butadiene. Morepreferably, the rubber particle is a polybutadiene. In said morepreferred embodiment, the rubber modified SAN polymer is a so-called ABS(acrylonitrile/butadiene/styrene) terpolymer. Generally, the continuousSAN matrix can be prepared from a monomer mix containing from about 15to about 50 percent by weight acrylonitrile based on the weight ofmonomers. The rubber content of the rubber modified SAN polymer canrange from about 0.1 to about 50, preferably from about 5 to about 20percent by weight of the rubber modified polymer.

Suitable styrene/acrylic acid copolymers include those which arepolymers of a monomer mixture containing from about 15 to about 50percent acrylic acid based on weight of monomers. Such polymers formmiscible blends with the oxazoline polymer in all proportions.

Diverse epoxy or phenoxy resins form miscible blends with the oxazolinepolymer in a wide range of proportions. Most generally, epoxy resins areoxirane-containing monomers or prepolymers comprising the reactionproduct of epichlorohydrin and an active hydrogen containing compound.Such epoxy resins prepared from bisphenol A typically have havemolecular structures as represented by the structures ##STR3## Thoseepoxy resins having structures corresponding to structure III, orsimilar structures, are generally high molecular weight thermoplasticresin. Blends prepared from such thermoplastic resins are alsothermoplastic. Epoxy resins having terminal oxirane groups, such asdepicted in structure IV, are curable with heating and the addition of acuring agent such as a polyamine, oxyalkylated short chain polyamine,polyamidoamine and the like. Blends of this invention containing suchcurable epoxy resin are usually crosslinkable (thermosettable) byincorporating such a curing agent into the blend. In addition, theso-called phenol novalac and epoxy cresol novalac resins are usefulherein. Preferably, however, the epoxy is a high molecular weightpolymer thermoplastic polymer as described herein.

Such epoxy and phenoxy resins are widely commercially available. Methodsfor the preparation, curing and use of such epoxy resins are describedin Sherman et al. "Epoxy resins" Kirk-Othmer Encyclopedia of ChemicalTechnology, 3rd Ed., Vol. 9, pages 267-290 (1980).

Vinylidiene chloride polymers and copolymers thereof, especiallycopolymers thereof with vinyl chloride, form miscible blends withoxazoline polymers when said blend contains at least about 45 percent byweight of oxazoline polymer based on the combined weight of thevinylidiene chloride and oxazoline polymer.

Similarly, styrene/acrylic acid (SAA) polymers which are polymerizedfrom a monomer mixture containing from about 5 to 15 weight percentacrylic acid form miscible blends with oxazoline polymers when the blendcontains about 0 to 60 weight percent of oxazoline polymer. It is noted,however, that as the acrylic acid content of the SAA copolymerdecreases, the copolymer forms miscible blends only with decreasingamounts of oxazoline polymer. For example, a SAA polymer containing 8percent acrylic acid forms miscible blends containing up to 60 percentof the oxazoline polymer. By contrast, a SAA polymer containing 5percent acrylic acid forms a miscible blend only when the blend containsabout 25 percent or less of the oxazoline polymer.

In addition to the polymers specifically described herein, the blends ofthis invention may comprise any other polymer which is capable offorming a miscible blend with the oxazoline polymer. The ability of anyparticular polymer to form a miscible blend with the oxazoline polymeris easily tested by blending a small quanity of the polymer being testedwith the oxazoline polymer in the desired proportions and determiningthe T_(g) of the blend so obtained.

In addition to the oxazoline polymer and at least one other comisciblepolymer, the blends of this invention may further contain or be blendedwith diverse materials such as other polymers, inert fillers,plasticizers, pigments, antioxidants, mold release agents,preservatives, and the like. The benefical use of such materials is wellunderstood by those skilled in the relevant arts.

Crosslinking agents are also beneficially, but optionally, employed inthe blends of this invention. Various materials are known to crosslinkoxazoline polymers including diisocyanates, as described in U.S. Pat.No. 4,087,413 to Kelyman et al. In addition, crosslinking agents whichcrosslink the other polymer contained in the blend are usefully employedin this invention

When an epoxy or other thermosetting resin is employed herein, the blendadvantageously contains a curing agent therefor.

The blends of this invention exhibit desirable physical and chemicalproperties which make said blends useful in a variety of applications,particularly membrane applications. Often, the physical properties ofthese blends are better than those exhibited by the oxazoline polymeralone. In addition, these blends usually exhibit increased waterwettability as compared to the nonoxazoline polymer alone.

A surprising aspect of the blends of this invention is that little ornone of the oxazoline polymer contained therein is extractable from theblends with water. This property is unexpected in that oxazolinepolymers are known to be readily soluble in water and are extractablefrom blends with another polymer which is not miscible with theoxazoline polymer. Generally, less than 25, preferably less than 10,weight percent of the oxazoline polymer in the blend is extractable withwater. Most preferably, less than about 5 weight percent of theoxazoline polymer is extractable from the blend.

Because the oxazoline polymer is not readily extracted from the blendsof this invention, the blends are suitable for use in aqueousenvironments or in contact with mixtures of water and alcohols or otherpolar organic molecules which are not solvents for the other polymers inthe blend. It is noted, however, that 2-oxazoline polymers are sometimesextractable from miscible blends with alcohol or mixtures of alcohol anda minor amount of water.

The blends of this invention typically exhibit a refractive indexintermediate to those of the component polymers. Accordingly, the blendsof this invention can often be prepared such that the blend has acertain desired refractive index. This is especially significant in thepreparation of certain rubber-modified polymers, where clarity isimproved by employing a polymer and rubber which have the samerefractive index. Using the blends of this invention, the refractiveindices of the polymer matrix and the rubber particles can be matched toyield a rubber-modified polymer with improved clarity. In particular,blends of 2-oxazoline polymers and a SAN polymer may be employed to formsuch higher clarity rubber-modified polymers.

The blends of this invention are especially useful as semi-permeablemembranes. Semi-permeable membranes are those which are readilypermeated by certain materials but which are substantially impermeableto other materials. Accordingly, said membranes are useful forseparating or concentrating the components of a fluid mixture (i.e.,mixtures of liquids or gases).

More particularly, the blends of this invention are useful forseparating the components of a fluid mixture of two or more organiccompounds in a pervaporation process. In said pervaporation process, oneside of the membrane (the feed side) is contacted with a fluid mixturecontaining two or more components. A pressure gradiant is providedacross the membrane so that the permeate side of the membrane is at alower pressure than the feed side. From the permeate side of themembrane is withdrawn a vaporous permeate which contains a higherconcentration of one component than is contained in feed mixture.General procedures for such pervaporation process are described in U.S.Pat. Nos. 3,950,247 and 4,035,291 to Chiang et al. Generally, thepermeate side of the membrane is maintained at a pressure lower than thevapor pressure of the major component of the permeate. The permeate sideof the membrane may be subjected to pressure as low as 0.1 mm ofmercury. In addition, superatmospheric pressure may be applied to thefeed side of the membrane. The temperature at which the separations areconducted affects both the selectivity and permeation rate. As thetemperature increases, the permeation rate rapidly increases whileselectivity decreases slightly. This increase in rate, however, may becompensated for by the increase in energy needed to maintain the systemat an elevated temperature. In general, the temperature is sufficientlyhigh that the components of the permeate have a substantial vaporpressure at the temperature at which the separation is effected andsufficiently low that the membrane is stable. Advantageously, thetemperature is from about -10° C. to about 95° C.

The membrane of this invention is useful in separating water fromorganic compounds which are miscible with water. Exemplarywater-miscible compounds include, but are not limited to, aliphaticalcohols, such as methanol, ethanol, propanol, hexanol, and the like;ketones, such as ethylmethyl ketone, acetone, diethyl ketone, and thelike; aldehydes, such as formaldehyde, acetaldehyde and the like; alkylesters of organic acids such as ethylacetate, methyl propionate, and thelike; p-dioxane; alkyl and cycloalkyl amines and other water-miscibleorganic compounds which do not chemically react with or dissolve themembrane of this invention. In addition, the organic compound may be onein which water has limited solubility, such as chlorinated alkanes likechloroform and carbon tetrachloride. Preferably, the organic compound isan aliphatic alcohol, a ketone or an aldehyde, with lower alcohols,especially ethanol, being preferred.

In addition, the membrane of this invention is useful in separatingmixtures of organic compounds particularly mixtures of a relativelypolar organic compound with a less polar organic compound. The organiccompounds in said mixture are preferably comiscible compounds but may beonly partially miscible. Exemplary organic mixtures which can beseparated with the membrane of this invention include, for example,mixtures of aliphatic alcohols with aromatics or alkanes, such asethanol/benzene, ethanol/hexane, methanol/hexane, propanol/toluenemixtures; methanol/methyl acetate, isopropanol/ethyl acetate,methanol/acetone, ethanol/ethyl acetate and like mixtures. A wide rangeof mixtures of compounds may be separated using the membrane of thisinvention provided that such mixture does not substantially dissolve orreact with the membrane under the conditions at which the separation iseffected.

The following examples are provided to illustrate the invention and arenot intended to limit the scope thereof. All parts and percentages areby weight unless otherwise indicated.

EXAMPLE 1

This example illustrates miscible blends of polyethyloxazoline (PEOX)with a rubber-modified styrene/acrylonitrile (ABS) resin. The resinemployed is a polybutadiene modified resin containing 13.5 weightpercent rubber dispersed in a continuous SAN matrix. The average size ofthe rubber particles is 0.5 microns. The continuous SAN matrix isprepared from a monomer mixture containing 25 weight percentacrylonitrile.

Blends are prepared by melting the ABS and PEOX polymers together in anoil-heated Brabender mixer at 190° C. for 10 minutes. In this manner,blends containing 0, 20, 40, 60 and 80 percent PEOX are prepared.

The glass transition temperature (T_(g)) of each of the blends isdetermined using a Perkin-Elmer DSC-2 calorimeter. The heating rate is20° per minute. The T_(g) is defined as the intersection of the heatcapacity slopes of the glassy and transition regions. In preparingsamples for the DSC, a weighed amount of the blend is placed in a taredDSC aluminum dish and then heated on a hot plate at about 200°-230° C.for 30 seconds to melt the blends. The melted sample is then cooled inthe DSC dish and evaluated in the calorimeter.

Moldings are prepared from the blends by grinding, followed bycompression molding. The ground polymer is preheated for 3 minutes at190° C. in the compression mold followed by heating for 3 minutes underfull pressure. The molding is cooled under pressure.

The molded blends are all clear or only slightly hazy. Each of theblends exhibits only one T_(g), indicating that such blends of PEOX andABS resins are miscible in all proportions.

In addition, a blend containing 10 percent PEOX and 90 percent ABS resinis prepared and molded as described above. This molding exhibits atensile strength at rupture of 5500 psi, 33 percent elongation atrupture, a modulus of 3.2×10⁻⁵ psi and a notched Izod of 3.2 lb/min.

EXAMPLE 2

Blends of a styrene/acrylic acid (SAA) copolymer (20 percent acrylicacid) and PEOX containing 0, 20, 40, 60 and 80 percent PEOX are preparedand molded as described in Example 1. In each case a clear molding isobtained. The T_(g) of each of the blends is determined by DSC asdescribed in Example 1. In each instance, the blend exhibits only oneT_(g).

Blends of an SAA polymer (containing 8 percent acrylic acid) areprepared containing 0, 20, 40, 60 and 80 percent PEOX. The blendscontaining 40 percent or less PEOX are clear. Those containing 60 and 80percent PEOX are hazy. The T_(g) of each of the blends is determined.Those blends containing 60 percent or less PEOX exhibit a single T_(g)and are accordingly examples of this invention. Those containing greaterthan 60 percent PEOX exhibit two T_(g) 's and are, therefore, notmiscible blends. Accordingly, these immiscible blends are not examplesof this invention.

A SAA polymer containing 5 percent acrylic acid is blended with PEOX atvarying proportions as described herein. Miscible blends are formed whenthe blend contains less than about 30 weight percent PEOX.

EXAMPLE 3

Blends of polyethyloxazoline and vinylidene chloride/vinyl chloridecopolymer (13.5 percent vinyl chloride; M_(w) =10,100) containing 0, 20,40, 60 and 80 percent PEOX are prepared by dissolving the PEOX andvinylidene chloride copolymer in tetrahydrofuran (THF) at 60° C. withstirring. The polymers are precipitated with n-heptane and dried undervacuum at 60° C. for 5 days. The blends containing greater than 50percent PEOX exhibit a single T_(g) and are accordingly examples of thisinvention. The blends containing less than 50 percent PEOX exhibit twoT_(g) and are, therefore, not miscible blends.

EXAMPLE 4

Blends are prepared by dissolving PEOX and a thermoplastic phenoxy resinsold as TKHH resin by Union Carbide Corporation in THF at roomtemperature. Blends containing 20, 40, 60 and 80 percent PEOX areprepared in this manner. Films are prepared from such blends by castinga film of the dissolved blend and then evaporating the solvent. Theblends all exhibit a single T_(g) indicating that the PEOX and thephenoxy resin are miscible in all proportions.

EXAMPLE 5

In this example, polyethyloxazoline (M_(w) equal 400,000) is meltblended with diverse SAN resins having various AN contents. Theresulting blends are compression molded as described hereinbefore andthe T_(g) of the molded blends is determined by DSC. The polymeremployed in the blends and the results obtained are as described in thefollowing table.

                  TABLE                                                           ______________________________________                                                                            T.sub.g                                                                       (Miscible                                                                     Blends)                                   Polymer % AN.sup.1                                                                            % PEOX.sup.2                                                                              Miscibility.sup.3                                                                     °C.                                ______________________________________                                        SAN-8    8      Immiscible in all proportions                                 SAN-16  16      Immiscible in all proportions                                 SAN-21  21      25          Yes     95.5                                      SAN-21  21      50          Yes     76.4                                      SAN-21  21      75          Yes     70.3                                      SAN-25  25      20          Yes     85                                        SAN-25  25      40          Yes     70                                        SAN-25  25      60          Yes     62                                        SAN-25  25      80          Yes     58                                        SAN-40  40      20          Yes     90                                        SAN-40  40      40          Yes     78                                        SAN-40  40      60          Yes     69                                        SAN-40  40      80          Yes     62                                        ______________________________________                                         .sup.1 Weight % Acrylonitrile repeating units in SAN polymer                  .sup.2 Weight percent polyethyloxazoline in blend. The polyethyloxazoline     has a molecular weight of 400,000, except those blended with SAN 16 and 2     which have a molecular weight of 606,000.                                     .sup.3 "Yes" indicates that the blend exhibits only one T.sub.g.         

From the foregoing Table it is seen that SAN polymers form miscibleblends with PEOX in all proportions provided the SAN polymer contains atleast about 18 percent acrylonitrile repeating units.

The sample of the blend containing 60 percent SAN (24 percent AN) and 40percent PEOX is extracted with water in an attempt to remove the PEOXcontent therefrom. A weighed dry sample of the molded blend (1.25 by1.25 by 0.01 cm) is extracted with 10 g of water for 3 days at roomtemperature under mild agitation. The thus treated sample is then driedand weighed to determine the amount of PEOX which is extracted from thewater. Under these conditions, no PEOX is extracted from the blend.Substitution of 10 percent of the water with ethanol leads to extractionof 8 weight percent of the PEOX in the blend. Forty-four percent of thePEOX is extracted with a 50/50 ethanol water solution.

A membrane is prepared from the blend containing 60 percent SAN (24percent AN) and 40 percent PEOX by melt blending and compression moldingas described above. The membrane has a thickness of 5 mils.

The membrane is placed onto an in-line filter holder so that a 14.2 cm²section of the membrane is open to feed solution. The membrane issupported with Whatman #50 filter paper. The permeate end of the filterholder is connected to a vacuum pump with two cold traps placed in lineto collect the permeate by condensation. The membrane and holder arethen immersed in a closed flask containing the mixture to be separated.The flask is equipped with thermometer for measuring temperature and areflux condenser to prevent feed loss due to evaporation.

Separation is effected by pulling a vacuum of about 0.1 mm Hg on thepermeate side of the membrane and collecting the permeate in the coldtrap. The temperature of the feed solution is maintained at 35° C. Thepermeation rate is calculated by periodically weighing the collectedpermeate. The permeate composition is determined by gas chromatographyusing a Hewlett-Packard 5840A gas chromatograph equipped with a thermalconductivity detector.

The membrane is used to separate various ethanol/hexane mixtures. Eachseparation is effected until a steady state condition is obtained(typically about 25 hours). Once a steady state is reached, the contentof the permeate and permeation rate are determined. The feed solution isa mixture of 7.3 percent ethanol and 92.7 percent hexane. The permeatecontains 97.7 percent ethanol. The separation factor α_(e) defined as:##EQU1## is determined to be 539. The permeation rate of this membraneis 174 g-ml-/m² -hr.

The foregoing separation is repeated, this time employing a membranewhich is a blend of 60 weight percent SAN resin (40 percent AN) and 40percent PEOX. In this case, the feed contains 7.5 percent ethanol and92.5 percent hexane and the permeate contains 99.5 percent ethanol,yielding an α_(e) of 2,454. The permeation rate is 31 g-mil/m² -hr.

For comparison, the foregoing separation is repeated this time employinga membrane comprising 100 percent SAN resin (40 percent AN). The feedcontains 7.4 percent ethanol and 92.6 percent hexane and the permeatecontains 2 percent ethanol yielding an α_(e) of 0.2. The permeation rateis 24 g-mil/m² -hr. These data clearly demonstrate the surprising effectcaused by the presence of PEOX in the separation membrane. The SAN resinalone exbibits a modest selectivity for hexane over ethanol. Bycontrast, the modified membrane of this invention exhibits a very highselectivity for ethanol over hexane. Moreover, the permeation ratesobtained with the membrane of this invention are significantly higherthan those obtained with the SAN membrane alone. The α_(e) values forthe membranes of this invention are extremely high. By contrast, thehighest reported literature value for α_(e) in an ethanol/hexaneseparation for an memembrane is 8.0.

What is claimed is:
 1. A semipermeable membrane comprising a blend or alloy of a first polymer which is a polymer of a 2-oxazoline and at least one other polymer which is not a polymer of a 2-oxazoline which other polymer is miscible with the first polymer at the relative proportions contained in the membrane, wherein the weight ratio of the first polymer and the other polymer is from about 19:1 to 1:19.
 2. A membrane of claim 1 wherein the 2-oxazoline is represented by the formula: ##STR4## wherein R is halogen or an inertly substituted lower alkyl group, each R¹ is hydrogen, an inertly substituted or phenyl or an inertly substituted low alkyl, and x is 1 or
 2. 3. The membrane of claim 2 wherein the 2-oxazoline is 2-ethyl-2-oxazoline.
 4. The membrane of claim 2 which membrane is a pervaporation membrane.
 5. The membrane of claim 1 wherein said other polymer is a styrene/acrylonitrile copolymer containing from about 18 to about 50 percent repeating acrylonitrile units.
 6. The membrane of claim 1 which is cross-linked. 